2 - Node 1 (one for the network and one for the heartbeat)
2 - Node 2 (one for the network and one for the heartbeat)
1 - Cluster group (for the clusterip)
1 - MSDTC group (for the msdtcip - Always use a seperate MSDTC group!)
1 - Per SQL Server instance (= virtual server - You can install multiple instances on a cluster and keep active/passive)
__ +
7 - So you need a minimum of 7 IP addresses.